Full
disclosure here, I'm a tube guy. I was raised on Dynaco. I've had the same
JoLida amp for 22 years. Sure I've listened to solid-state amps in my life, even
had some in my home, but I've always gravitated back to those therimonic
devices. Maybe I'm just brainwashed Dynascum. Maybe if I get a chance to hear
one of Nelson Pass's well-received amps or a 47 Lab Gaincard I might change my
mind, but right now that's where I plant my flag. And this brings me to my
review of the Linear Tube Audio ZOTL10 MK II stereo vacuum tube amplifier. Yet
first....

Of course valve-powered amps vary quite a bit. My
listening experiences have ranged from the intimidating 200 Wpc Conrad Johnson
Premier One to the always-lovable 3.5 Wpc Fi 2A3
'X' amplifier (reviewed here). But no matter
what the design, all of them had output transformers so they could talk
correctly to the speakers. No transformer is perfect. Even the very best ones
have inherent distortions. It has been one of those tradeoffs in life. I love
being able to haul all sorts of stuff in my minivan, but I'm never going to beat
a Ferrari off the line when the light turns green.

All of Linear Tube Audio's amplifiers are
designed by David Berning. Some people think he's a genius. Harvey
"Gizmo" Rosenberg thought he was an alien who came down to enlighten
us. Berning created and patented the ZOTL topology. He still personally builds
his amplifiers under the Berning name, just like Dan Garber did with fi.
I can't imagine how much soldering that man has done in his lifetime. But one
man can only solder so much. That's were LTA has given poor Mr. Berning a break.
Their equipment is made right here in the USA with his guidance. You may not own
an amplifier personally made by its creator, but it's pretty darn close.

Now ZOTL stands for zero-hysteresis output
transformer-less. Say that ten times fast and you win a lollypop. Now, I can
look at a schematic of a simple single-ended or push-pull amp and I figure out
what's going on. As soon as I look at a schematic of a ZOTL amp, I am lost.
There is great explanation of ZOTL in an old issue of Glass
Audio
magazine I'd recommend if you are really interested. I read it several
times and I think I know what's going on, but don't hold me to that.

As soon you take the ZOTL10 MK II out of the box, you
notice how light it is. Duh, no output transformers! Even the separate power
supply isn't heavy. Oh yeah, the separate power supply, that's where the Mk II
designation comes from. You have to connect the amp to the power supply with a
short umbilical. Easy-peasy. On the back there are two sets of inputs, one for
using the volume control on the front, and one for bypassing it. Also in the
back are sturdy binding posts, which were a little close together for my
cumbersome Audio Magic speaker cables. Unlike many amplifiers, the ZOTL10 MK II is
deeper that wide, so when I slid it into my modest stereo cabinet, it barely fit.

Now about the looks. If you like to show off to
your friends that you have a tube amp, you might be a little disappointed. The
front is a large square of brushed aluminum, a volume knob and a blue
"power on" LED. The guts are covered by black perforated metal cover
that more than reminds of me of the cover on my old Dynaco ST70. Turn it on,
peer inside, and yup there they are, pretty glowing vacuum tubes. Luckily I'm a
secure tube owner, so just knowing they are in there doing their job is fine. If
anyone doubts me, they can take a peek for themselves.

Peering inside, the ZOTL10 looks more like UNIVAC
than a traditional tube amplifier. Two 12AT7s and two 12AU7s are used in the
driver/splitter stage and four EL 84s are used in push-pull configuration as the
output tubes. Those of you who are guitar-amp geeks know that EL 84s were
responsible for the British-blues sound in the 1960's. They also further evoke
the Dynaco comparison. Back in the day, Dynaco had the ST-35, which was EL 84
based. The more famous ST-70 used the bigger EL34s. The big brother ZOTL40 uses
EL34 vacuum tubes also. Coincidence? I think not.

Back to the insides. The 12AT7s and 12AU7s are
NOS; the EL 84s are the new Genalex Gold Lions from New Sensor in Russia. Using
these tubes as standard equipment demonstrates a dedication to quality. It's too
bad that there aren't more NOS power tubes out there anymore. A set of EL 84
Bugle Boys would be nice. I'm sure Keith Richards has a stash somewhere. Oh
well, one can dream. There are no biasing adjustments needed since the ZOTL10 MK
II is
self-biasing. This is about as much plug-and-play as it comes.

Whenever you listen to a truly great piece of
equipment, it shows you its greatness right out of the box. This is definitely
the case with the ZOTL10 MK II. As normal in my home, there were several family
members wandering through the living room when I was hooking things up. I just
happened to have Imogen Heap's Ellipse [Epic ‎– 88697 506052]
laying around, so I put it on. The first track First Train Home started
playing. My son, who happened to be walking by, stopped in his tracks.

"Is that the new amp?"

"Yup."

"It sounds so … smooth."

"You're right."

"How long do you get to keep it?"

"Until I'm done reviewing it."

Pause. "Well take your time, this sounds great."

It's good to know that your own flesh and blood
appreciates some of the same things you do. But what elicited that reaction? I've
had many different pieces of gear in my home and never before has anyone had
such a visceral response. My wife and eldest daughter acted quite the same way.
(My youngest always give a shrug) How can I even quantify this? One of my
favorite Gizmo quotes is, "Once we get the hang of the words, we lose their
meaning." I'll try my best.

I know it's sort of boring to talk about, but let's
talk about the ZOTL10's performance across the frequency spectrum, starting with
the bass. I have never heard a tube amp, check that - any amp, in my home
with such deep, tuneful, freaking POWERFUL bass. Remember, this is 12 WPC! More
about that later.

Lorde's Melodrama [Republic –
602557725070] is chocked full of great bass lines. At the beginning of the
second verse of Green Light, some of that deep, tickle-you-in-the-loins
bass kicks in. Whoa, where the heck did that come from? I didn't even know my
old Thiels could get there. Who needs a sub when you have this testubular bass?
Ok, let's move on to the midrange, sticking with Lorde's catharsis. The vocals
on this album are intimate; up front with no reverb. There she is, front and
center, growling out her pain. Hey, you don't have to scream when you are in
pain. That growl, it comes up from her chest, reverberates in her mouth, and
hisses over her exposed teeth. Despite this tortuous path, the ZOTL10 MK II never
turns her vocals into Parseltounge. Lorde's natural hiss is enough. This is
single-ended triode midrange territory guys.

This benevolent nature extends to the high
frequencies also. Recordings that I had thought previously as "too
screechy", like Snow Patrol's Fallen Empires [Fiction Records –
2786192], are suddenly tamed. There is absolutely no listening fatigue. The best
I can describe it is like a really good 2A3 amp. That good. On top of that,
there's a seamlessness. None of the frequency ranges get preferential treatment.
Leopold Stokowski Encores [London Records – 433 876-2] is not what you
would consider an audiophile disc. I've listened to it many a time and thought
I knew its sonic flaws. Playing it through the ZOTL10, the string basses
have a new fullness, but they are never bloated, the woodwinds have new tonal
richness, and the violins are suddenly singing. This is a revelation.

I think another reason that the ZOTL10 MK II elicits
such a gut reaction is the way it avoids smearing the subtle musical cues that
you experience in a live performance. Steven is his review of the 47
Labs Gaincard perfectly described this property as "rhythmically
musical freedom". I've never had a chance to hear an Audio
Note UK Ongaku or the Gaincard, but I suspect this is what we have been
hearing at our home since the ZOTL10 MK II arrived. Everything just flows like real
music. James Horner's Pas de Deux [Mercury Classics ‎– 481 1487
DH] is a pleasurable listen because of the interplay between the violin and
cello played by the Samuelsen siblings. What is it about family members playing
together?

Listening to this performance through the ZOTL10
MK II,
you can feel the back and forth between brother and sister; listening to
each other in a way that only people who have played years together can. It's a
thing of beauty. Another example of this is Bill Evan's Waltz for Debbie
[Analogue Productions – 0009], where you can feel the jam between the
members of this trio. Sitting there, I kept finding myself gently swaying or
nodding, caught up in the rhythm. Evans, LaFaro, and Motian at times might seem
like they were each doing their own thing, but then they all come together,
letting you know that they had it under control all the time.

Now let's go into a paradigm shift here folks.
The ZOTL10 MK II is a push-pull type amp. As typical, this amp employs negative
feedback to lower the distortion. This tends to do two things, introduce a
time-phase shift which blurs some of the musical cues, and flattens out the
dynamics. As I said in the previous paragraph, the ZOTL10 MK II swings like crazy.
Dynamically the ZOTL10 MK II is as free-wheeling as any SET I've heard. Looking
through my old vinyl, I pulled out Brahms' Second Piano Concerto [Resonance –
2535 263]. This is lower-priced re-issue of a Karajan / BPO recording with
GezaAnda at the piano. Not exactly the stuff of audiophile fetishes. Playing it
through the ZOTL10, I'd never heard this recording so dynamic and alive. Just
what the heck is going on here? I admit it, I've become a bit of a curmudgeon in
the last few years of my life. I'd become convinced there was only one path to
audio enlightenment, but now ZOTL has shown me an alternate path. That's the
funny thing about life, no matter how old you get, you can still learn
something.

Now before I wrap things up, let's touch on one
more topic -- power. How much power do you need? I know some of you saw that 10
Watts and thought, "Well, that's not going to work for me." I listened
to the ZOTL10 through my 4-Ohm Thiel CS1.5s, so the rated power output was 12
Wpc. As I have mentioned before, the Thiels are not the most sensitive of
speakers at 86dB/W/m. Sounds like a poor match, doesn't it? Wrong. Never did I
feel like the ZOTL10 was running out of steam. If you want to rock out to Muse
or Foo Fighters, be my guest. You don't need to crank it up to "11" to
get that killer bass you crave. This amp gives it to you at lower listening
levels than you're used to. As long as you don't plan on pairing them with some
hard-to-drive planar speakers, electrostatics, or giant arrays, you should be
fine.

As you already guessed by now, I am smitten with
the ZOTL10 MK II. Its brings out the best in any music you play through it. Rock,
jazz, classical, pop – it doesn't matter. What made it so difficult to review
this amp is the reviewer part of my brain would keep shutting off and I would
just start listening to the music. I can't think of any better compliment than
that. Now if I could just get my hands on some Bugle Boys, we could go to the
next level of enlightenment.